Every serious bullying incident I ran into growing up ended when a kid got popped in the mouth. Every unserious bullying incident made no impact when I knew if it got serious, I could pop them in the mouth and likely come out on top.
I've met way too many adults with personality issues that were a product of adults telling child them "physical violence is always wrong, just tell an adult, be the bigger person" etc. It always needs to be taught as a last resort, and it needs to be understood that even justified violence comes with consequences and other tools must be used first, but when you've done everything you're supposed to and no one is helping to the resolve the problem, sometimes you have to do it yourself.
It ain't pretty, and it ain't ideal, but it's the way it is.
Ngl this was my first thought. Or dig out a pair of those ol' soap shoes and do a sick grind (practice first with both of these).